Hot oils or heat transfer fluids are used for the indirect heating of processes by circulating the heated fluid between hot oil boilers and reactor vessels, tanks, molds, calenders, extruders, or heat exchangers. Such fluids are subjected to temperatures ranging from 300.degree. F. (149.degree. C.) to 750.degree. (399.degree. C.) for heating applications in the chemical, plastics, rubber, petrochemical, pharmaceutical, pulp and paper, textile, and food industries.
It is known to incorporate filters into such systems to remove contaminates from the fluid. See, for example, U.S. Pat. Nos. 5,484,523; 5,264,119; 5,022,986 and 4,272,368. None of the filter housings described therein disclose or suggest the structure of the closure plate as described herein.
U.S. Pat. No. 5,484,523 shows a centrally positioned sleeve projecting from the inside of the cover and externally threaded to engage an internally threaded top end of a filter. This arrangement undesirably requires the steps of threading successive filters to the sleeve on the cover and of unthreading the filters from the cover when replacing filters.
U.S. Pat. No. 5,264,119 shows a filter support to be mounted in a cylindrical cavity formed in the head plug of the filter. The filter support is glued into place to prevent leaks and displacement of the filter support during maintenance. The head plug may be attached to a bearing plate which is the closure for the top of the filter housing.
The filter assembly of U.S. Pat. No. 5,022,986 has a cap with a downwardly directed cylindrical rib projecting into the upper end of the filter and an ear extending downward adjacent the inside of the filter. The cap is secured to the housing and engages the entire top of the filter.
U.S. Pat. No. 4,272,368 discloses an end closure for a filter housing which is a cup-shaped member having a center tubular projection which serves as a support member for the filter element. The cup-shaped member is either attached to the housing or to another member in order to provide closure for the housing.
It is known to provide filter elements specifically tor the filtration of hot oils at temperatures up to 700.degree. F. (371.degree. C.) and pressures up to 150 psig (1034 kPa). These filter elements, as in the present invention, are installed in housings that comprise a top closure plate and a filter housing. The closure plate is a blind flange removably connected, as by bolts, to a top flange on the filter housing, with a gasket between the closure plate and the top flange.
The filter housing has two compartments: an upper dirty chamber and a lower clean chamber. An imperforate bottom plate separates the two chambers. Liquids enter the housing through the upper chamber and then pass through a filter element and drain into the lower chamber.
The filter element, as in the present invention, consists of filter media wound on a perforated core. In the prior art, the filter element is installed on a rigid, perforated standpipe with an exteriorly threaded upper end and a bolt and washer are used to secure the filter element to the standpipe and hold the filter element in place, with the bottom end of the standpipe being threaded and screwed into a threaded hole in the bottom plate. FIG. 1 shows a filter housing assembly according to the prior art.
The filter elements must be periodically replaced during normal operation. Removal of a filter element requires removal of the closure plate, only after the filter has cooled and the pressure inside the housing has been relieved.
Several problems exist with the above-described conventional filter housing assembly. First, the cost of the bolt and of threading both ends of the standpipe is unnecessary. Second, the time and effort required to remove the bolt before removing a filter is unnecessary. Third, the closure plates of the prior art filter housings used for processing hot oils provide no protection from direct sprays of hot and pressurized liquid due to gasket failure, or improper sealing or misalignment during installation of the closure plate. Fourth, the filter element and the standpipe supporting the filter element lean under the very high pressures of liquid entering the upper chamber. This unnecessarily increases the difficulty of replacing a filter element.